inferior oblique

The shortest extraocular muscle and the only one that does not arise at the back of the orbit. It begins on the front inner part of the orbital floor beside the tear duct, passes backward and outward beneath the inferior rectus, and inserts behind the equator on the lower temporal part of the globe, close to the macula. Its primary action is extorsion, with elevation and abduction as subsidiary actions^1,2.

With the eye turned inward by 51 degrees it becomes a pure elevator, which is its test position (up and in)^1,2. Its antagonist is the superior oblique, and the inferior division of the oculomotor nerve supplies it^2,3. Overaction, seen as an upshoot of the eye when it turns inward, usually accompanies a superior oblique palsy or infantile esotropia.